It is known that by-product liquid condensates from the production of gas (natural gas, associated gas) and crude oil can contain many trace metal compounds in the trace state, generally present in the form of organometallic complexes, in which the metal forms bonds with one or more carbon atoms of the organometallic radical.
These metal compounds are poisons of catalysts used in the processes of transformation of petroleum. In particular, they poison the catalysts of hydrofining and hydrogenation by gradually being deposited on the active surface. Metal compounds are located in particular in the heavy cuts coming from the distillation of crude (nickel, vanadium, arsenic, mercury) or else in natural gas condensates (mercury, arsenic).
The thermal cracking or catalytic processing of the above hydrocarbon cuts, for example, their steam cracking for conversion into lighter hydrocarbon cuts, can make possible the elimination of some metals (for example, nickel, vanadium . . . ); on the other hand, some other metals (for example, mercury, arsenic . . . ) able to form volatile compounds and/or being volatile in the element state (mercury) are at least partly in the lighter cuts and can thereby poison the catalysts of the subsequent transformation processes. The mercury further presents the risk of causing corrosions by forming amalgams, for example, with the alloys with an aluminum base, in particular in the sections of the processes operating at a sufficiently low temperature to cause the condensation of liquid mercury (cryogenic fractionations, exchangers).
Prior processes are known for eliminating mercury or arsenic in gas phase hydrocarbons; the procedure is performed in particular in the presence of solid masses, which can equally be called: adsorption, collection, trapping, extraction, metal transfer masses.
Concerning the masses for demercurization: U.S. Pat. No. 3,194,629 describes masses consisting of sulfur or else iodine deposited on activated carbon.
U.S. Pat. No. 4,094,777 of the applicant describes other masses comprising copper at least partly in the form of sulfide and a mineral support. These masses can also contain silver.
French application 87-07442 of the applicant describes a specific method of preparation of said masses.
Patent FR 2534826 describes other masses consisting of elementary sulfur and a mineral support.
Concerning the dearsenification:
Patent DE 2149993 teaches the use of metals of group VIII (nickel, platinum, palladium).
U.S. Pat. No. 4,069,140 describes the use of various absorbent masses. Supported iron oxide is described, the use of lead oxide is described in U.S. Pat. No. 3,782,076 and that of copper oxide in U.S. Pat. No. 3,812,653.
Now, if some of the products described in the prior art exhibit good performances for the demercurization or else for the dearsenification of gas (for example, hydrogen) or gas mixtures (for example, natural gas) and more particularly when the natural gas contains a large amount of hydrocarbons containing three or more than three carbon atoms, the tests made by the applicant show that the same products prove not very effective as soon as the batches contain compounds other than elementary metals, for example, for arsenic, arsines comprising chains containing hydrocarbon containing two or more than two carbon atoms or else, for mercury, dimethyl mercury and other mercury compounds comprising chains containing hydrocarbon containing two or more than two carbon atoms, and optionally other nonmetal elements (sulfur, nitrogen . . . ).
Further, other tests carried out by the applicant show that when sulfur is present in the batch, it can interact with active metal elements for the dearsenification which, then at least partly transformed into sulfides, can then present a significant loss of activity.
The object of the invention is a process of eliminating mercury and optionally arsenic contained in a batch containing hydrocarbon and which eliminates defects of the prior processes.
Another object of the invention is to be able to eliminate mercury and optionally arsenic even in batches containing hydrocarbon further containing significant proportions of sulfur. By significant proportions, 0.005 to 3% by weight, and in particular 0.02 to 2% by weight, is meant.
According to the process of the invention, a mixture of the batch and hydrogen is made to pass in contact with a catalyst that below will arbitrarily be called arsenic collection mass, with catalytic properties, containing:
at least one metal M of the group formed by iron, cobalt, nickel, palladium and platinum; PA1 at least one metal N of the group formed by chromium, molybdenum, tungsten and uranium; PA1 and optionally an active phase support, with a base of at least one porous mineral matrix, said catalyst being followed on the path of the batch of, or mixed with, a mercury collection mass, containing sulfur and/or at least one metal sulfide with at least one metal P selected from the group formed by copper, iron and silver, and an active phase support. PA1 activates by catalysis the compounds of mercury and arsenic (if arsenic is present) and transforms them into reactive compounds relative to collection masses, object of the invention, PA1 selectively collects arsenic (if arsenic is present), PA1 activates by catalysis said mercury compounds even in the strict absence of arsenic compounds.
According to another embodiment of the invention, it is also possible to add a sulfur compound; for example, an organic sulfide or else hydrogen sulfide, either in the crude batch (before dearsenification), or in the batch treated in the presence of hydrogen and the dearsenification mass with catalytic properties, before demercurization in the presence of the second bed.
When the batch also contains arsenic, the latter is also eliminated. The procedure is performed preferably with the batch at least partly in liquid phase.
It has also been discovered, in a surprising way, that in the presence of high concentrations of arsenic or else in the presence of high "liquid" hourly volumetric rates able to cause an imperfect collection of arsenic (for example, less than 90%) on the arsenic collection mass with catalytic properties, the mercury collection mass also operates in a very satisfactory manner for the collection of arsenic.
Finally, it has been discovered that, in a surprising manner, the catalyst also makes possible a hydrodesulfuration, a hydrodenitrification and, at least partly, a hydrogenation of unsaturated compounds able to be located in the batch, which can prove advantageous when said batches are intended for steam cracking. Finally, said mass makes possible an effective demetallization if, besides arsenic and mercury, vanadium and/or nickel are present.
In a surprising way, the catalytic properties of said arsenic collection mass remain unchanged, even in the case of the strict absence of said metal in the batch.
Said arsenic collection mass with catalytic properties is therefore a complex solid, which, in the presence of hydrogen and under the operating conditions described below:
The arsenic collection mass with catalytic properties designated below as "the catalyst" entering into the composition of the whole being the object of this invention therefore consists of at least one metal M selected from the group formed by iron, nickel, cobalt, palladium, platinum and at least one metal N selected from the group formed by chromium, molybdenum, tungsten and uranium, these metals, in the form of oxides and/or oxysulfides and/or sulfides, able to be used just as they are or preferably to be deposited on at least one support of the following list. Under conditions of use, it is imperative that metal M and/or metal N are in sulfurated form for at least 50% of their whole.
It is known to one skilled in the art that the state of equilibrium between the reduced and sulfurated forms depends, among others, on the operating conditions and in particular, besides the temperature, on partial pressures of hydrogen, hydrogen sulfide, and steam in the reaction medium, e.g.: ##EQU1##
The respective amounts of metal or metals M and metal or metals N contained in the catalyst are usually such that the atomic ratio of metal or metals M to metal or metals N, M/N, is about 0.3:1 to 0.7:1 and preferably about 0.3:1 to about 0.45:1.
The amount by weight of metals contained in the finished catalyst expressed by weight of metal relative to the weight of the finished catalyst is usually about 2 to 30% and preferably about 5 to 25% for metal or metals N, and about 0.01 to 15%, more particularly about 0.01 to 5% for metal or metals M and preferably about 0.05 to 3% for palladium and/or platinum; and about 0.5 to 15% and preferably about 1 to 10% in the case of nonnoble metals M (Fe, Ca, Ni).
Of metals N, molybdenum and/or tungsten are preferably used, and of metals M, nonnoble metals iron, cobalt and/or nickel are preferably used. Advantageously, the following metal associations are used: nickel-molybdenum, nickel-tungsten, cobalt-molybdenum, cobalt-tungsten, iron-molybdenum and iron-tungsten. The most preferred associations are nickel-molybdenum and cobalt-molybdenum. It is also possible to use associations of three metals, for example, nickel-cobalt-molybdenum.
The porous mineral matrix is selected so that the final catalyst has optimum pore volume characteristics. This matrix usually comprises at least one of the elements of the group formed by alumina, silica, silica-alumina, magnesia, zirconia, titanium oxide, clays, aluminous cements, aluminates, for example, magnesium, calcium, strontium, barium, manganese, iron, cobalt, nickel, copper and zinc aluminates, mixed aluminates, for example, those comprising at least two of the metals cited above.
It is possible to prefer to use matrices containing alumina, for example, alumina and silica-alumina or else titanium oxide. When the matrix contains silica, it is preferable that the amount of silica be at most equal to 25% by weight relative to the total weight of the matrix.
In addition, the matrix can also contain at least one of the compounds cited above, at least one crystalline, zeolite aluminosilicate, synthetic or natural (zeolite). The amount of zeolite usually represents 0 to 95% by weight and preferably 1 to 80% by weight relative to the weight of the matrix.
It is also possible to use advantageously mixtures of alumina and zeolite or else mixtures of silica-alumina and zeolite.
Of the zeolites, it is usually preferred to use zeolites whose skeleton atomic ratio, silicon to aluminum (Si/Al), is greater than about 5:1. Zeolites with faujasite structures and in particular Y stabilized or ultrastabilized zeolites are advantageously used.
The most commonly used matrix is alumina, and transition and pure aluminas or aluminas in a mixture, such as .gamma..sub.C, .gamma..sub.T, .delta., .theta., are usually preferred.
Said matrix will preferably exhibit a large surface and a sufficient pore volume, i.e., or at least 50 m.sup.2 /g and at least 0.5 cm.sup.3 /g, for example, 50 to 350 m.sup.2 /g and 0.5 to 1.2 cm.sup.3 /g. The macropore volume fraction, consisting of all the pores of an average diameter at least equal to 0.1 micron, can represent 10% to 30% of the total pore volume.
The preparation of such a catalyst is sufficiently known to one skilled in the art not to be repeated in the context of this invention.
Before use, the catalyst can, if necessary, be treated by a gas containing hydrogen at a temperature of 50.degree. to 500.degree. C. It can also, if necessary, be presulfurated at least partly, for example, according to the French SULFICAT (R) process or else by treatment in the presence of a gas containing hydrogen sulfide and/or any other sulfur compound.
The mercury collection mass entering into the composition of the whole being the object of this invention consists of sulfur or a sulfur compound deposited on a support or porous mineral matrix selected, for example, from the group formed by alumina, silica-aluminas, silica, zeolites, clays, activated carbon, aluminous cements, titanium oxides, zirconium oxide or else from the other supports, consisting of a porous mineral matrix, cited for the catalyst.
It is possible to use, as collection mass, sulfur deposited on a support and, for example, a commercial product such as CALGON HGR, and more generally any product consisting of sulfur deposited on activated carbon or on a macroporous alumina as described in French patent 2534826.
A compound containing sulfur and a metal P, where P is selected from the group formed by copper, iron, silver and, preferably, by copper or the copper-silver association, will preferably be used. At least 50% of metal P is used in the form of sulfide.
This collection mass can be prepared according to the method recommended in U.S. Pat. No. 4,094,777 of the applicant or else by deposition of copper oxide on an alumina then sulfuration by an organic polysulfide as described in French patent application 87/07442 of the applicant.
The proportion of elementary sulfur combined or not in the collection mass is advantageously between 1 and 40% and preferably between 1 and 20% by weight.
The proportion of metal P combined or not in the form of sulfide will preferably be between 0.1 and 20% of the total weight of the collection mass.
The whole consisting of the catalyst and the mercury collection mass can be used either in two reactors or in a single one.
When two reactors are used, they can be placed in series, the reactor containing the catalyst being advantageously placed before the one containing the collection mass.
When a single reactor is used, the catalyst and the collection mass can be placed either in two separate beds or intimately mixed.
According to the amounts of mercury and/or arsenic (calculated in elementary form) contained in the batch, the volume ratio of the dearsenification mass with catalytic properties to the demercurization mass can vary between 1:10 and 5:1.
When the procedure is performed in separate reactors, the reactor containing the dearsenification mass with catalytic properties can be operated in a temperature range able to go from 180.degree. to 450.degree. C., more advantageously from 230.degree. to 420.degree. C. and preferably from 260.degree. to 390.degree. C.
The operating pressures will preferably be selected from 1 to 50 absolute bars, more particularly from 5 to 40 bars and more advantageously from 10 to 30 bars.
The hydrogen flow, expressed in liters of gaseous hydrogen (STP) per liter of liquid batch will preferably be selected between 1 and 1000, more particularly between 10 and 300 and more advantageously from 30 to 200.
The hourly volumetric rate, calculated relative to the dearsenification mass with catalytic properties, can be from 0.1 to 30 hours.sup.-1, more particularly from 0.5 to 20 hours.sup.-1 and preferably from 1 to 10 hours.sup.-1 (volumes of liquid, per volume of mass and per hour).
The demercurization mass will be operated in a temperature range able to go from 0.degree. to 400.degree. C., more advantageously from 20.degree. to 350.degree. C. and preferably from 40.degree. to 330.degree. C.
The operating pressures and hydrogen flow D will be those defined relative to the dearsenification mass with catalytic properties.
The hourly volumetric rate, calculated relative to the demercurization mass, can be that indicated for the dearsenification mass with catalytic properties, it being understood, as indicated above, that the volume ratio of the dearsenification mass to the demercurization mass can vary from 1:10 to 5:1 as a function in particular of the proportions of arsenic and mercury contained in the batch. Therefore, of course, the relative proportions of the two masses and therefore the hourly volumetric rates relative to the masses can then be very different (same liquid flow but different mass volumes).
In an embodiment of the invention, the batch treated in the presence of the catalyst can optionally be cooled before passing over the demercurization mass.
In another embodiment, the two collection masses then being placed in a single reactor, the latter can be operated in a temperature range able to go from 180.degree. to 400.degree. C., more advantageously 190.degree. to 350.degree. C. and preferably 200.degree. to 330.degree. C.
Finally, as it is known to one skilled in the art, it can prove advantageous to recycle at the head, at least partly, the hydrogen-rich gas recovered after separation of the purified liquid product. Besides a large reduction of the hydrogen consumption, said recycling makes possible a better control of the ratio of partial pressures pH.sub.2 S/pH.sub.2 in the reaction medium. As indicated above, for the case where the batch contains very little sulfur (for example, less than 20 ppm by weight), it can further prove advantageous to add in the batch and/or in the hydrogen at least one sulfur compound to increase said ratio pH.sub.2 S/pH.sub.2.
The batches to which the invention applies more particularly contain 10.sup.-3 to 2 milligrams of mercury per kilogram of batch and, optionally, 10.sup.-2 to 10 milligrams of arsenic per kilogram of batch.